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# AsyncIO Event Loop Issues in Gradio Applications ## Problem Summary When building Gradio applications that use async functions internally, you may encounter the error: ``` "Error in async execution: asyncio.run() cannot be called from a running event loop" ``` This occurs when `asyncio.run()` is called from within an already running event loop, which is common in Gradio applications since they run in their own event loop. ## Root Cause Analysis ### Why This Happens 1. **Gradio's Event Loop**: Gradio applications run within an existing asyncio event loop 2. **Nested Event Loops**: `asyncio.run()` creates a new event loop and cannot be called from within an existing one 3. **Async Function Wrappers**: Synchronous wrapper functions attempting to use `asyncio.run()` fail when called from Gradio's event loop ### Code Patterns That Cause Issues **❌ Problematic Pattern:** ```python def sync_wrapper(input_data): """This will fail in Gradio""" import asyncio try: result = asyncio.run(async_function(input_data)) # ❌ Fails in running loop return result except Exception as e: return {"error": f"Error in async execution: {str(e)}"} ``` **❌ Another Problematic Pattern:** ```python async def async_wrapper(input_data): """This also fails""" import asyncio result = asyncio.run(another_async_function(input_data)) # ❌ Still wrong return result ``` ## Solutions ### Solution 1: Proper Async/Await Pattern **✅ Correct Approach:** ```python async def async_wrapper(input_data): """Use await instead of asyncio.run()""" result = await async_function(input_data) # ✅ Correct return result ``` ### Solution 2: Thread Pool for Event Loop Isolation **✅ Robust Synchronous Wrapper:** ```python def sync_wrapper_for_gradio(input_data): """Handles event loop detection and isolation""" import asyncio import concurrent.futures try: # Try to get the current event loop loop = asyncio.get_event_loop() if loop.is_running(): # We're in a running loop - use thread pool with concurrent.futures.ThreadPoolExecutor() as executor: future = executor.submit( lambda: asyncio.run(async_function(input_data)) ) return future.result() else: # Safe to use run_until_complete return loop.run_until_complete(async_function(input_data)) except RuntimeError: # No event loop exists, create one return asyncio.run(async_function(input_data)) ``` ### Solution 3: Nest AsyncIO (Alternative) **✅ Using nest_asyncio:** ```python def sync_wrapper_with_nest_asyncio(input_data): """Enable nested event loops""" import asyncio import nest_asyncio # Enable nested event loops nest_asyncio.apply() try: result = asyncio.run(async_function(input_data)) return result except Exception as e: return {"error": f"Error: {str(e)}"} ``` ## Implementation Details ### File: `app.py` Lines 1796-1831 The fix implemented in this project uses the Thread Pool approach: ```python def process_with_config_sync(text_input, uploaded_file, provider, model, api_url, api_key): """Synchronous wrapper for Gradio that properly handles async calls.""" import asyncio import nest_asyncio # Enable nested event loops (important for Gradio) try: nest_asyncio.apply() except: pass # nest_asyncio might not be available try: # Try to get the current event loop loop = asyncio.get_event_loop() if loop.is_running(): # If we're in a running loop, we need to use create_task import concurrent.futures # Create a new event loop in a thread pool with concurrent.futures.ThreadPoolExecutor() as executor: future = executor.submit( lambda: asyncio.run( process_with_config_async(text_input, uploaded_file, provider, model, api_url, api_key) ) ) return future.result() else: # We can safely use run_until_complete return loop.run_until_complete( process_with_config_async(text_input, uploaded_file, provider, model, api_url, api_key) ) except RuntimeError: # No event loop exists, create one return asyncio.run( process_with_config_async(text_input, uploaded_file, provider, model, api_url, api_key) ) ``` ## Key Changes Made 1. **Removed `asyncio.run()` from async functions** - Lines 1371, 1785 2. **Replaced with proper `await` calls** in async contexts 3. **Created thread-pool-based synchronous wrapper** for Gradio compatibility 4. **Updated Gradio event handlers** to use the synchronous wrapper ## Testing and Validation After implementing the fix: - ✅ No more "cannot be called from a running event loop" errors - ✅ Gradio interface functions correctly - ✅ Async functions execute properly within the application - ✅ Real-time progress updates work as expected ## Prevention Guidelines 1. **Never use `asyncio.run()` inside async functions** 2. **Use `await` for calling async functions from async contexts** 3. **For Gradio integration, use thread pool isolation for sync wrappers** 4. **Test with both standalone and Gradio-hosted execution** 5. **Consider using `nest_asyncio` for simpler cases** ## Dependencies for Solutions ```txt # For thread pool approach (built-in) concurrent.futures # Standard library # For nested event loops approach nest-asyncio>=1.5.0 ``` ## Related Issues - Gradio applications with MCP server integration - FastAPI + Gradio hybrid applications - Jupyter notebook environments with existing event loops - Any application mixing sync and async patterns ## References - [Python AsyncIO Documentation](https://docs.python.org/3/library/asyncio.html) - [Gradio AsyncIO Compatibility](https://gradio.app/docs/) - [nest_asyncio Package](https://pypi.org/project/nest-asyncio/)